The present invention relates to the technical field of plastics and adhesives technology, more particularly the adhesive bonding of edges, more particularly plastics edges or edge bands.
The present invention relates more particularly to a method for applying edges, more particularly plastics edges, to materials, and also to the products produced in this way, and to the use thereof.
The present invention further relates to a method for applying adhesive layers which can be activated by means of laser radiation to edges, more particularly to edge bands. The present invention likewise relates, moreover, to edge bands which can be provided on at least one side with an adhesive layer which can be activated by means of laser radiation.
Lastly, the present invention relates to the inventive use of a composition for equipping an edge band with an adhesive layer.
In the prior art there are a multitude of methods known for mounting edge bands onto the narrow faces of in particular panel-like workpieces.
Typically, in the prior art, edge bands are mounted onto the narrow faces of panel-like workpieces in through-travel machines, such as, for example, edge-processing machines, with the aid of edge gluing assemblies. In this case provision is generally made for the narrow face of the workpiece to be furnished, immediately prior to the placement of the edge band, with a hot-melt adhesive, more particularly with so-called “hotmelts”.
The mounting of the edge bands in through-travel machines, with application of hot-melt adhesive immediately prior to the placement of the edge band, is a cost-effective method which is also suitable for producing relatively large numbers of units. Nevertheless, this method harbours a multiplicity of disadvantages.
For instance, the melting of the hot-melt adhesive is energy-consuming and leads overall to an increase in the operating costs; a time of up to half an hour, for example, elapses before an operating temperature of 150 to 210° C. is attained. Furthermore, energy is needed to head the glue container in order to maintain the adhesive in the liquid or application-ready state throughout the production process. Adhesive application takes place usually by means of spraying, jetting, rolling or knife coating onto the workpiece.
Moreover, the above-described method requires relatively large amounts of the adhesive. As a consequence, after solidification, the adhesive joint becomes more susceptible to penetration by dirt and moisture, and so, over the course of time, on the one hand the adhesive bond may become undone, and on the other hand the adhesive edge is often unsatisfactory from an aesthetic standpoint.
In addition, the use of the adhesive in such large amounts leads to swelling of adhesive out of the bonded joint during subsequent pressing of the edge band onto the workpiece, and such swelling results in instances of fouling both of the workpiece and of the processing machine. To prevent this, the workpiece must be treated with release agents—a costly and inconvenient procedure—before the method is commenced.
Moreover, it is possible in this way to process only those hot-melt adhesives that have relatively low molecular weights and relatively high melt indices, which, however, do not always lead to the desired bonding qualities.
Because of the disadvantages of this method, as set out above, a search has been ongoing for some considerable time into alternative possibilities for the mounting of edge bands onto narrow faces of panel-like workpieces.
Other prior-art methods attempt to avoid these disadvantages through provision of edge bands already coated with adhesive, which allow subsequent mounting onto the narrow face at any desired point in time following the application of adhesive.
In order to produce edge bands already coated with adhesive, there are a variety of methods known in the prior art. While such methods do lead to an improvement in relation to the disadvantages identified above, and do allow, in particular, a more flexible regime, they are nevertheless unsatisfactory in a host of respects.
One way of producing precoated edge bands is by coextrusion. In that case, thermoplastic edge bands are produced in what are called inline processes, with a subsequently activatable plastics layer or adhesive layer—in other words the production of the edge band on the one hand and its furnishing with plastics or adhesive on the other take place, as it were, simultaneously. By means of coextrusion it is also possible to process polymers having a particularly high molecular weight, thus leading to particularly stable adhesive bonds. Nevertheless, this method is hampered by numerous disadvantages.
Coextrusion methods necessitate particularly high levels of investment in relation to the production line, since said line must always be adapted individually to the particular process. This technology is therefore economical only for large production runs and batches; the production of individual embodiments which are not sold in large volumes, in particular, often makes no sense from the economic standpoint.
Furthermore, such methods also carry numerous disadvantages in a technical respect. The reason is that, with coextrusion methods, the direct joining of thermoplastic edge tape and plastics layer or adhesive layer has to take place without the use of an adhesion promoter. In the absence of the adhesion promoter layer, consequently, sufficient adhesion can be achieved only between materials of the same kind. In addition, the use of, for example, resin-impregnated paper edges or veneer edges as an edge band is not possible, since only thermoplastic materials are extrudable.
All in all, therefore, there is only a very limited selection of materials, or limited selection of combinations of materials, that can be used for producing precoated edge bands.
As well as the production of coated edge bands by coextrusion, it is also possible to coat edge bands with a hot-melt adhesive, or hot melt, as part of offline processes. In the case of these methods, the edge band per se is produced first of all, and only later on, by a toll coater or a manufacturer of furniture parts, for example, is it coated with a subsequently activatable adhesive. All in all, such offline processes offer good flexibility in relation to the edge materials that are to be coated, and, by virtue of the cost-effective regime, allow the furnishing of small batches and production runs as well: as is the case for the coated edge bands produced by coextrusion, the activation or ultimate bonding of the edge, more particularly plastics edge, to the respective materials component may take place at any desired period following completion of the coated edge band. Nevertheless, even methods of this kind are associated with serious disadvantages. A particular problem is that the use of polymers with high molecular weights and low melt indices is not possible, since the high temperatures that this requires cannot be achieved in offline operation. Though it is possible to coat the edge bands much more cost-effectively in such offline processes, the resultant adhesive bonds are nevertheless inferior in terms of service properties to the edge bands produced by coextrusion, and are comparable merely with the conventional edge gluing using thermoplastic hot melts, as has been described above.
The melting of the adhesive layer, both of edge bands produced by coextrusion and of aftercoated edge bands, for the subsequent mounting of the edge band onto a material, is normally accomplished by means of hot air or of infrared, UV, laser, plasma or microwave radiation. In such cases, however, the transfer of energy to the adhesive is often only weakly pronounced or poorly controllable, and so the heating is relatively lengthy or unspecific. Furthermore, in view in particular of the poor controllability, the edge band itself is frequently heated as well. This, however, is detrimental to the quality of the edge band, since heating of the edge band can lead to physical damage, resulting in turn in the edge band materials being restricted to those that lack sensitivity.
For example, EP 1 163 864 A1 describes furniture panels and a method for producing them, with provision being made for a thermoplastics edge produced by coextrusion and having layers of different hardnesses to be melted by means of hot air or laser radiation and mounted onto the furniture panel, comprising a wood-based material. As already described above, however, the use of coextrusion for producing coated edge bands has a multitude of disadvantages. In the absence of an adhesive layer based on high molecular mass polymers, moreover, the stability and quality of the adhesive bond produced in this way are unsatisfactory.
Moreover, DE 10 2006 021 171 A1 describes cover strips based on thermoplastics that are likewise produced by coextrusion and as part of their production process are provided with a hot-melt adhesive layer which can be activated by laser radiation. This method as well is associated with the above-described general disadvantages of coextrusion methods.
WO 2009/026977 A1 describes edge strips for furniture items that have a melting layer which can be activated with supply of energy, the coated edge strip being produced by coextrusion. The resultant adhesive joints, however, have a relatively high thickness of up to 1.5 mm, and this—as likewise described above—on the one hand is unwanted, in view of aesthetic considerations, and on the other hand may lead to more rapid soiling and/or parting of the adhesive layer. In particular, the relatively thick adhesive layer means that it is impossible to achieve targeted and efficient reactivation of the adhesive.